Advances in mass spectrometry, due primarily to new desorption techniques, have made it possible to analyze peptides without prior derivatization. Characterization of the covalent structure for a peptide requires more than simply determining the amino acid sequence. Modification of the peptide structure may be due to changes occurring during chemical synthesis of the peptide or may be due to post-translational processing occurring during biosynthesis. Both types of modifications can alter the biological activity of the particular peptide. Identification of theme structural changes is necessary for a thorough understanding of the peptide's activity. Generation of structural and functional diversity as a consequence of post-translational modification has continued to be our interest. Prohormone processing is one particular type of post-translational processing that generates structural and functional diversity. Using two assays developed in our laboratory, we have isolated and purified several putative neuropeptide precursors from bovine pituitary and hypothalamus extracts. We continue our search for novel neuropeptides that may arise by post-translational processing of prohormone precursors.